Transtissue drug delivery is a non-invasive therapeutic method in which a drug is first placed onto a tissue of a host animal and then caused to penetrate into the tissue in furtherance of the desired therapeutic treatment. Transtissue drug delivery can be used to treat topical, local, or systemic medical conditions. Delivery can occur across a number of different tissues including the skin, mucosal membranes, oral tissue, or the like. Delivery through the skin is generally referred to as “transdermal” drug delivery.
Transdermal drug delivery is typically accomplished by using a covering element in the form of a transdermal patch device that is attached to the host at the desired drug delivery site. A typical transdermal patch structure includes a drug-in-adhesive layer sandwiched between an impermeable backing and a release liner. At the time of use, the release liner is easily removed so that the patch can be attached to the host, adhesive side down. The impermeable backing thus traps the drug-in-adhesive layer between the backing and the attachment site of the host. Over time, the drug penetrates into the host, or is topically active, in accordance with the desired therapeutic treatment. Optionally, the drug-in-adhesive formulation may include one or more compounds known as penetration enhancers that increase the delivery of the drug to the subject.
Although the peel and place type of transdermal drug delivery device has been an extremely effective means to accomplish drug delivery for a wide variety of medical conditions, there are still a number of ways in which transdermal drug delivery, and transtissue drug delivery in general, could be improved. For instance, the structure of the conventional peel and place patch currently involves a manufacturing operation requiring the drug-in-adhesive to be coated onto a substrate, e.g., the impermeable backing or the release liner, as the case may be. This kind of coating step involves substantial expense in terms of capital equipment, utilities, manufacturing space, and human resources needed to carry out the coating operation. To avoid such expense, it would be desirable to design an alternative, or to eliminate entirely the need for such a coating step.
Furthermore, the use of a release liner creates an item of waste in the sense that the release liner must be discarded in some fashion after being removed from the patch. It would be desirable to provide a more environmentally-friendly alternative, or to avoid this kind of waste entirely.
Transtissue drug delivery could further be improved if customized patches were to be made whose drug concentration or rate of delivery was custom tailored to the needs of individual patients. Currently, it is not economically feasible to do this, because patches of a particular drug formulation are typically made in large numbers using mass production techniques. Consequently, patch manufacturers typically formulate transtissue delivery patches to be generally efficacious for the population as a whole. Of course, this approach has been and will continue to be effective in many instances, but some situations exist in which a treatment could be optimized, and patient suffering further alleviated, by a customized patch formulation.
Furthermore, transtissue drug delivery would be improved if the rate of drug delivery could be more effectively controlled. That is, initially, when the concentration of the drug in the patch is still relatively high, current patches generally deliver the drug at a relatively high rate. However, as the concentration of the drug in the patch is depleted, the rate of drug delivery generally slows down. Thus, the efficiency of current patches generally and undesirably varies over time. A patch that is characterized by a steady, consistent rate of drug delivery over a longer period of time would provide a more optimal treatment option in some instances.
Finally, currently available transtissue delivery systems are not particularly “user-friendly.” That is, the application of a transdermal patch requires many steps; unwrapping of the patch, peeling away of the release liner and disposal of the release liner and wrapper. Additionally, some of the larger-sized conventional patches may be uncomfortable to wear since they may not conform easily to the contour of the body. As a result, movement of the area where the patch is located may cause discomfort.